Droplets, Droplets

Was finally able to see some controlled droplet formation.

It was with a PDMS-glass chip (width 50µm, height 25 µm) designed and fabricated by my research lead, YG, at Cal. The design was intended to generate and incubate single cells, which could be of proximate length-scales as micro-droplets. YG was kind enough to let me attempt droplet generation with his chip.

There were three inlets, two for water streams angled at a Y-geometry that met an oil stream perpendicularly. The two water streams first met each other prior to being sheared off at the junction by the carrier oil phase.

Starting at 200 µL/hr of oil flow rate (Qoil) & 35 µL/hr of water flow rates (Qwater), only parallel flows of water and oil streams were initially observed. With Qwater fixed, Qoil was then increased incrementally (to 210 µL/hr, 250 µL/hr, 280 µL/hr, etc), until droplets started forming. After stable formation of droplets was observed, Qoil was then decreased to see if droplets could be formed at lower oil flow rates. The main difference appeared to be the length of the droplets, with higher relative Qoil forming shorter droplets, as was expected based on reviews of various relevant literature[Ref: 1,2,3].

Time has also been allotted to work on my 1st year report, which is due in mid-Nov, also working alongside an undergraduate student on making new masters/devices for various designs that YG wants to get made; it is a good transition practice to pick up the microfabrication protocol here. I also look forward to attending a cell culture workshop that trains on handling live cells. The plan next week is to learn COMSOL to model velocity profiles in microchannels, to quicky acquire/flush out prelim. ideas on geometry designs that would better control separation of individual droplets. Have also been re-acquainting with AutoCAD on modifying channel designs, mainly learning to incorporate winding microchannels for incubation of cell-droplets.

Coming up next also includes focusing literature reviews on cell trapping & benchmark these for project ideas.

References
[1] Tan, Y.C., Cristini, V. & Lee, A. Monodispersed microfluidic droplet generation by shear focusing microfluidic device. Sens. Actuators, B 114, 350-356 (2006)
[2] Zheng, B., Tice, J.D. & Ismagilov, R.F. Formation of droplets of alternating composition in microfluidic channels and applications to indexing of concentrations in droplet-based assays. Anal. Chem.76, 4977-4982 (2004)
[3] Tice, J.D. et al. Formation of droplets and mixing in multiphase microfluidics at low values of the Reynolds and the Capillary numbers. Langmuir 19, 9127-9133 (2003)